1. Field of the Invention
The present invention relates to an optical control type phased array antenna apparatus, and in particular, to an optical control type phased array antenna for receiving a plurality of radio wave signals coming in predetermined directions and/or transmitting radio wave signals in predetermined directions, by using an optical signal processor by means of Fourier transform processing a high-frequency signal in an optical space, without executing any digital signal processing.
2. Description of the Prior Art
FIG. 16 is a block diagram of an optical control type phased array antenna apparatus of a first prior art disclosed in the Japanese Patent Laid-Open Publication No. 3-044202.
Referring to FIG. 16, an optical radiator 101 splits a beam of light radiated from a laser diode provided inside the optical radiator 101, into two branched beams of light. One branched beam of light is directly outputted as a first beam of light 103, while the frequency of another branched beam of light is shifted by the frequency of a radio signal inputted from an oscillator 102, and then the frequency-shifted another branched beam of light is outputted as a second beam of light 104.
The first beam of light 103 radiated from the optical radiator 101is incident on an image mask 106 via a mirror 105 and is transmitted through the image mask 106. The image mask 106 transforms the incident first beam of light 103 into a beam of light 107 corresponding to the beam shape of a desired antenna radiation pattern such as a sectoral beam pattern, and then, radiates the transformed beam of light to a Fourier transformation lens 8. Then, the Fourier transformation lens 8 subjects the incident beam of light 107 to spatial Fourier transformation so as to radiate a beam of light 109 of a beam width d after the transformation to a beam combiner 10. On the other hand, the second beam of light 104 radiated from the optical radiator 101 is radiated to a distribution adjuster 131. The distribution adjuster 131 adjusts the width of the second beam of light 104 to a predetermined beam width, and then, radiates the second beam of light after the adjustment as a reference beam of light 132 to the beam combiner 10. The beam combiner 10 mixes and combines the beam of light 109 from the Fourier transformation lens 8 with the reference beam of light 132 from the distribution adjuster 131, and thereafter, radiates a combined light 111 of a beam width d to a fiber array 12.
The fiber array 12 is comprised of a plurality of M sampling optical fibers arranged parallel to one another on a plane so that the lengths of the sampling optical fibers are arranged parallel to one another at predetermined intervals, and the combined light 111 incident on the fiber array 12 is spatially sampled to be incident on the sampling optical fibers. Beams of light incident on the sampling optical fibers are made incident on photoelectric converters 14-1 to 14-M via M optical fiber cables 13-1 to 13-M. Each of the photoelectric converters 14-1 to 14-M photoelectrically converts the incident beam of light into a radio signal which has a frequency of a difference between the first beam of light 103 and the second beam of light 104 and whose amplitude is proportional to the amplitude of the inputted beam of light and whose phase coincides with the phase of the inputted beam of light. Thereafter, the photoelectric converters 14-1 to 14-M output the resulting signals, respectively, to antenna elements 17-1 to 17-N arranged parallel to one another in a straight line or on a plane via power amplifiers 15-1 to 15-M and feeder lines 16-1 to 16-M. With this arrangement, a radio signal is radiated into a free space with a radiation pattern which is previously set by the image mask 106.
Furthermore, an attempt at processing a signal received by an array antenna with a high-frequency signal processed in an optical space (referred to as a second prior art hereinafter) is disclosed in a prior art document of G. A. Koept, "Optical processor for phased array antenna beamforming", SPIE477, pp. 75-81, May, 1984.
However, the optical control type phased array antenna apparatus of the first prior art shown in FIG. 16 has had such a problem that the incoming radio wave signal cannot be received and such a problem that a plurality of radio signals cannot be radiated. Furthermore, the second prior art disclosed in the above-mentioned prior art document has had such a problem that a plurality of signals cannot be received. Furthermore, each of the first and second prior arts is constructed of a beam combiner, and therefore, they have had such a problem that an aligner adjustment for making the optical axes coincide with one another is hardly achieved, and the size of the optical processing system becomes larger.